The present invention relates to means for improving fuel economy of a multi-cylinder internal combustion engine followed by an automatic transmission through a hydrokinetic unit.
It is known, for the purpose of improving fuel economy, to operate a multi-cylinder internal combustion engine on selected cylinders of all under light load.
In the case of a multi-cylinder internal combustion engine followed by an automatic transmission via a hydrokinetic unit, such as a torque converter or a hydraulic coupling, if the engine runs on selected cylinders of all, the engine is likely to halt when the vehicle is brought to a standstill with a selector lever of a selector valve in a "drive" range. This is because, under this condition, the engine revolution speed is low and a certain load is imposed on the engine via the hydrokinetic unit. It therefore is the conventional practice to operate the engine on all of the cylinders to assure vibration free smooth engine operation at idling speed. The fact that, when the engine idles, all of the cylinders are brought into operation is not favourable from the point of view of cutting off fuel consumption.
A conventional apparatus or cylinder selector for operating a 6-cylinder internal combustion engine on selected three cylinders of all is shown in FIG. 2 and FIG. 1 shows a diagram explaining operation modes of the engine provided with the apparatus shown in FIG. 2. In this diagram, the pulse width W.sub.p of a fuel injection signal is against the engine revolution speed(RPM) N.sub.E.
The operation modes are as follows:
(1) The engine runs on 6 cylinders when the engine speed N.sub.E is lower than a predetermined level or value N.sub.EO because at such low engine speeds the engine might vibrate if it runs on 3 cylinders.
(2) When the engine speed N.sub.E is higher than the predetermined level N.sub.EO, the number of cylinders on which the engine run is controlled as follows by comparing the actual pulse width of fuel injection signal W.sub.p with two predetermined levels W.sub.PH and W.sub.PL (W.sub.PH &gt;W.sub.PL).
(a) The engine runs on 6 cylinders (6-cylinder mode) when W.sub.p is greater than the higher predetermined level W.sub.PH.
(b) The engine runs on 3 cylinders when the pulse width W.sub.P is smaller than the lower predetermined level W.sub.PL.
(c) When the pulse width W.sub.P plunges into the intermediate range between the higher and lower predetermined levels W.sub.PH and W.sub.PL from the range above or greater than the higher predetermined level W.sub.PH, the engine continues to run on 6 cylinders until the pulse width W.sub.p becomes smaller than the lower predetermined level W.sub.PL. When the pulse witdh W.sub.p plunges into the intermediate range between the higher and lower predetermined levels W.sub.PH and W.sub.PL from the range below or smaller than the lower predetermined level W.sub.PL, the engine continues to run on 3 cylinders until the pulse width W.sub.p becomes greater than the higher predetermined level W.sub.PH.
Explaining the apparatus of FIG. 2, an engine intake air flow sensor 1 and an engine revolution sensor 2 are provided to produce outputs representing the intake air flow, in quantity, and representing the engine revolution speed(RPM), respectively. These outputs from the sensors 1 and 2 are fed to a fuel injection control unit 3 which produces a fuel injection signal whose pulse width representing the engine load of the engine under the control. Comparators 4, 5 and 6 are provided together with two pulse width level adjusters 7 and 8 and an engine revolution speed level adjuster 9. The comparator 4 compares the pulse width signal W.sub.p with a high predetermined pulse width level signal W.sub.PH and produces a high level signal "1" only when W.sub.p is greater than W.sub.ph (W.sub.p &gt;W.sub.PH), while, the second comparator 5 compares the signal W.sub.P with a low predetermined pulse width signal W.sub.PL and produces a high level signal "1" when W.sub.P is greater than W.sub.PL (W.sub.P &gt;W.sub.PL). The comparator 6 determines the engine revolution speed from the frequency of pulses of the fuel injection signal from the fuel injection control unit 3 and compares the engine revolution speed signal N.sub.E with a predetermined engine revolution speed level N.sub.EO to produce a high level signal "1" when N.sub.E is greater than N.sub.EO (N.sub.E &gt;N.sub.EO). The outputs from these comparators remain at a low level signal "0" outside of the predetermined conditions as above. An OR circuit 10 and an AND circuit 11 are provided. The output from the comparator 4 is fed to one of two inputs of the OR circuit 10 and the output from the comparator 6 is fed to the other input of the OR circuit 10 through an inverter 13. The output from the comparator 6 is fed to one of two inputs of the AND circuit 11 and the output from the comparator 5 is fed to the other input of the AND circuit 11 through an inverter 12.
The output of the OR circuit 10 is fed to "S" (set) terminal of a flip-flop circuit 14 and the output of the AND circuit 11 is fed to "R" (preset) terminal thereof. When W.sub.P &gt;W.sub.PH and/or N.sub.E &gt;N.sub.EO, a high level signal "1" appears as the output from the OR circuit 10 and a low level signal "0" appears outside this condition. Meanwhile, a high level signal "1" appears as the output from the AND circuit 11 when W.sub.P &gt;W.sub.PL and N.sub.E &gt;N.sub.EO and a low level signal "0" appears outside this condition. The flip-flop circuit 14 produces at its Q output terminal a high level signal "1" when the engine operating condition is within a 6-cylinder region diagrammatically illustrated in FIG. 1 and continues to produce the high level signal "1" until the engine operating condition falls into 3-cylinder region shown in FIG. 1. When the engine operating condition has fallen into 3-cylinder mode, the output on the Q terminal switches to a low level signal "0" and this low level signal "0" will be maintained until the engine operating condition falls into the 6-cylinder mode range shown in FIG. 1. The Q output is fed to one of two input terminals of an AND circuit 15 whose the other input terminal receives the fuel injection signal from the fuel injection control unit 3. When a high level signal "1" appears on the Q output terminal of the flip-flop circuit 14, the AND circuit 15 will permit the passage of the fuel injection signal therethrough toward a terminal 16 operatively connected with fuel injection nozzles adapted to supply fuel to cylinders #1 to #3 so that under this condition the fuel injection nozzles for these cylinders inject fuel in response to fuel injection signal from the fuel injection control unit 3. Since the fuel injection signal is always supplied via terminal 17 to three fuel injection nozzles for the other three cylinders #4 to #6, the engine operates on 6 cylinders under this condition. When the signal on the Q output terminal of the flip-flop circuit 14 switches to a low level signal "0", the AND gate 15 is closed to prevent the passage of fuel injection signal therethrough toward the terminal 16 so that fuel injection to cylinders #1 to #3 will be suspended. Thus, under this condition, the engine runs on 3 cylinders #4 to #6.